With regard to a semiconductor device such as a ULSI, if a particle-shaped foreign material (hereinafter, referred to as “particle”) adheres to its surface, a short circuit may be caused, rendering the semiconductor device inoperable. Therefore, it is necessary to perform an inspection of whether a particle exists on a surface of the semiconductor device in a course of manufacturing it, for example, in a plasma processing system. Such inspection has been conventionally conducted by using an apparatus 150 for inspecting a surface of an object to be processed (hereinafter, referred to as “object surface inspection apparatus”) using a laser scattering method, as shown in FIG. 15.
The object surface inspection apparatus 150 irradiates a laser beam to an inspection site on the surface of a wafer W mounted on a rotatable and vertically movable stage 151 from a laser beam illuminator 152 disposed above the stage slantwise. Then, a scattered light detector 153 disposed above the stage 151 detects a scattered light, which might be generated in case a particle adheres to the inspection site, and an operation unit 154 connected to the scattered light detector 153 analyzes the detected scattered light. If it is determined by the object surface inspection apparatus 150 that there exists a particle on the surface of the wafer W, the operation of a corresponding manufacturing line is stopped, and cleaning of the manufacturing line is performed in order to prevent a reduction in the yield of semiconductor devices in the manufacturing line.
At this time, a scratch, which is a polishing damage occurred on the surface of the wafer W, also generates a scattered light when a laser beam is irradiated thereto. Accordingly, even when there is no particle on the surface of the wafer W, the object surface inspection apparatus 150 erroneously determines that there is a particle due to the presence of the scratch. As a result, an unnecessary cleaning of the manufacturing line is performed, which decreases the operating rate of the manufacturing line.
For the above reason, there has been developed an object surface inspection apparatus capable of determining whether a defect on the wafer surface is a particle or a scratch. Known as such inspection apparatus is an object surface inspection apparatus using a dimensional characteristic of a scratch that it has a depth much smaller than its width (see, for example, US Patent Application Publication No. 2002/0122174 A1). This object surface inspection apparatus uses the fact that the quantity of scattered lights generated by an irradiation of an incident light to the scratch in a direction oblique to the wafer surface is smaller than the quantity of scattered lights generated by an irradiation of an incident light in a direction normal to the wafer surface.
However, as circuits formed on a semiconductor device become finer recently, the size of particles to be inspected is also becoming finer to the extent that they have the same size as microscopic defects (for example, voids or cracks) in a resist film formed on a wafer surface. Accordingly, it is necessary to distinguish the particles and the microscopic defects. Since, however, the microscopic defects have a depth substantially identical to or greater than its width and have a shape different from the scratch, the conventional object surface inspection apparatus cannot be used to distinguish the particle and the microscopic defect.